Between his upcoming Fox series and the highly anticipated Full House spin-off, John Stamos is having a particularly busy 2015 – which is what made the news that the he’d checked himself into a residential program for the treatment of substance abuse all the more shocking to his co-workers.
Those who have worked with Stamos, 51, call him “lovely,” “charming” and “always professional,” but after his June 12 DUI arrest, a pal told PEOPLE that the actor’s drinking had been a “problem” in the past.
A source close to Stamos adds that the death of his mother, Loretta, last September “did a number on him. It s been a hard time.”
But after entering treatment in late June, Stamos is “focusing on his health,” says the source.
“He has a big year ahead of him,” continues the source. “And he knows he needs to take care of himself.”
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For more on Stamos’ decision to seek treatment, pick up this week’s issue of PEOPLE, on newsstands Friday