Montana shared that Clark had asked him to speak at his funeral before he died.
"I had a few choice words for him, which I can't say in church," Montana said.
He also noted, "I'm not one for usually writing things down, but I won't lie, this is probably one of the toughest things I've ever had to do."
Other family and 49ers legends spoke at Clark's memorial service. Click here for a look.
STORIES & VIDEOS ABOUT CLARK
- 49ers great Dwight Clark dies at 61 after battle with ALS
- Funeral service for 49ers legend Dwight Clark held at Grace Cathedral in San Francisco
- 'One of the toughest things I've ever had to do': Joe Montana remembers Dwight Clark
- 'I know he loved me, and I sure loved him': Eddie DeBartolo gives eulogy at Dwight Clark memorial
- 'He was the most wonderful father': Daughter remembers 49ers legend Dwight Clark at memorial in San Francisco
- 49ers' Brent Jones remembers Dwight Clark at private memorial service in San Francisco
- 'He carried that passion': Brother, niece remember Dwight Clark at memorial
- South Bay sports community reflects on Dwight Clark's passing
- Friends, fans react to death of 49ers legend Dwight Clark
- San Francisco 49ers honor Dwight Clark at Levi's Stadium in Santa Clara
- Mike Shumann honors teammate, friend, Dwight Clark after emotional reunion
- San Francisco 49er teammates react to Dwight Clark's ALS announcement
- Mike Shumann on former teammate Dwight Clark: 'There will never be another 87'
- VIDEO: Behind-the-scenes with 49ers 1981 championship team
- Lafayette man battling ALS offers support to 49ers legend Dwight Clark
- Former San Francisco 49ers WR Dwight Clark announced he has ALS
