Justin Bieber is in high spirits as he visits YouTuber David Dobrik near UCLA... after his Lyme disease and mono diagnoses

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He revealed on Wednesday that he had been diagnoses with both Lyme disease and chronic mononucleosis.

Justin Bieber seemed to be feeling good despite the recent diagnosis as he visited the YouTube star David Dobrik in Los Angeles' Westwood neighborhood on Thursday.

The 25-year-old pop star and his friend were deluged by a crowd of adoring fans from the nearby UCLA campus during their short meetup.

Standing tall: Justin Bieber, 25, seemed to be feeling good despite Lyme disease and chronic mono diagnoses as he visited YouTube star David Dobrik in LA's Westwood neighborhood on Thursday

Justin stood out on his afternoon outing in a hot pink hoodie that hung loosely on his frame.

He paired it with an equally baggy set of jeans and nondescript black sneakers.

The Sorry singer sported a mustache he'd started growing in the new year, and he repped his own Drew clothing brand with a brown trucker hat featuring the label's smiley logo.

Unmissable: Justin stood out on his afternoon outing in a hot pink hoodie that hung loosely on his frame

Low key: He paired it with an equally baggy set of jeans and nondescript black sneakers

Promotion: The Sorry singer sported a mustache he'd started growing in the new year, and he repped his own Drew clothing brand with a brown trucker hat featuring the label's smiley logo

Justin was a passenger in a white Tesla Model X, but he got out once he arrived in Westwood to greet his friend David.

The popular vlogger contrasted Justin's look with a black sweater and black pinstripe pants with tall socks and plain black sneakers.

The two pals embraced each other as Justin stepped out of the car.

Driving in style: Justin was a passenger in a white Tesla Model X, but he got out once he arrived in Westwood to greet his friend David

Back in black: The popular vlogger contrasted Justin's look with a black sweater and black pinstripe pants with tall socks and plain black sneakers

Friends: The two pals embraced each other as Justin stepped out of the car

For the people: After a crowd of students from UCLA had lined up on the sidewalk, Justin showed off gracious demeanor by taking selfies inside his Telsa with multiple people on the street

After a crowd of students from UCLA had lined up on the sidewalk, Justin showed off gracious demeanor by taking selfies inside his Telsa with multiple people on the street.

Then the Love Yourself singer did some self-promotion by dancing to his new single Yummy, which he released Friday in advance of his upcoming album and tour.

Justin seemed to revel in the attention, though it came at a difficult time for him.

He revealed only the day before that he had been diagnosed with Lyme disease, which is caused by a bacterium spread by blacklegged ticks and is common in the upper Midwest and Northeast regions of the United States.

Infected individuals can initially develop a rash around the bite site and suffer from headache, fatigue and fever.

Untreated forms of Lyme can also cause skin problems, joint paint and neurological issues. 

Busting a move: Then the Love Yourself singer did some self-promotion by dancing to his new single Yummy, which he released Friday in advance of his upcoming album and tour

Eating it up: Justin seemed to revel in the attention, though it came at a difficult time for him

Illness: He revealed only the day before that he had been diagnosed with Lyme disease, which is caused by a bacterium spread by blacklegged ticks

Justin defended his appearance and behavior in his Instagram post revealing his diagnosis.

'While a lot of people kept saying Justin Bieber looks like sh*t, on meth etc. they failed to realize I've been recently diagnosed with Lyme disease, not only that but had a serious case of chronic mono which affected my, skin, brain function, energy, and overall health,' he explained.

The singer–songwriter also announced that his upcoming YouTube docuseries would detail his struggles with Lyme disease and his treatment.

'You can learn all that I've been battling and OVERCOMING!!' he wrote, staying positive. 'It's been a rough couple years but getting the right treatment that will help treat this so far incurable disease and I will be back and better than ever NO CAP.'

Explained: Justin struck back at people who said he 'looks like sh*t' and is 'on meth,' attributing changes in his appearance to his diagnoses

Fighting it: The singer–songwriter also announced that his upcoming YouTube docuseries would detail his struggles with Lyme disease and his treatment

Road to wellness: 'You can learn all that I've been battling and OVERCOMING!!' he wrote, staying positive. 'It's been a rough couple years but getting the right treatment that will help treat this so far incurable disease and I will be back and better than ever NO CAP.'

Mystery solved: Fans and critics have remarked on Justin's skin and acne in recent years, which could be both a symptom of his Lyme disease and the chronic mono

Fans and critics have remarked on Justin's skin and acne in recent years, which could be both a symptom of his Lyme disease and the chronic mono.

Mono is caused by the Epstein-Barr virus and spreads through saliva, often via kissing.

Chronic mono occurs when the body's immune system isn't able to tamp down the initial infection, allowing the virus to remain active.

In addition to the common fatigue symptom, those with the chronic form of the illness can suffer liver damage, skin rashes, swollen lymph nodes, and have an enlarged spleen, among other symptoms. 

Blue moods: Justin had suffered bouts of severe depression throughout 2019, which could have been related to his acknowledged struggles with substance abuse in previous years

Hopeful: But the condition could also be influenced by his recent diagnoses, which may offer help in treating it

Justin had suffered bouts of severe depression throughout 2019, which could have been related to his acknowledged struggles with substance abuse in previous years.

But the condition could also be influenced by his recent diagnoses, which may offer help in treating it.

So far, Justin hasn't clarified when he might have caught the illness, though many Lyme disease suffers don't know when they've been infected because they ticks may be too small to easily spot.

Bella Hadid, Shania Twain and Avril Lavigne were all previously diagnosed with Lyme disease, as was designer Tommy Hilfiger's daughter Ally.

Fellow Canadian singer Avril offered her support following the announcement in a lengthy social media post.

'Today @JustinBieber shared that he has Lyme disease. There are too many people that have this debilitating disease!' she wrote. 

In good company: Bella Hadid, Shania Twain and Avril Lavigne were all previously diagnosed with Lyme disease, as was designer Tommy Hilfiger's daughter Ally 

Coming soon: Justin's upcoming documentary series will debut on January 27 and will air on Mondays and Wednesdays on YouTube

'People I love and care about and many friends and fans I have crossed paths with. To everyone affected by Lyme, I want to tell you that there is HOPE.

'Because Lyme is a daily struggle, for the better part of two years, I was really sick and fighting for my life. Writing #HeadAboveWater helped me get through the worst of it, but the bad days still come and go.' 

Justin has been helped with his mental health struggles and his new diagnoses by his wife Hailey Bieber, 23.

He and the model dated for two months starting in December 2015, before reunited in May 2018.

They got engaged in July and had a secret courthouse wedding in September 2018, before making it official with a larger wedding for family and friends in South Carolina on September 30 of last year.

Justin's upcoming documentary series will debut on January 27 and will air on Mondays and Wednesdays on YouTube.

Supportive: Justin's wife Hailey Bieber, 23, has been by his side as he struggled with depression throughout last year