Can you know the damage before teleporting with Cleric Peace Domain Lvl6 Protective Bond?

At level 6 when you get the ability to teleport to other bonded creatures to take their incoming damage do you get to know the damage value before you teleport?

For instance player1 is bonded to player2. If player2 is attacked by a goblin wielding a shortbow and the goblin rolls a successful attack. Can player1 wait until after the damage roll before deciding to use the reaction to teleport and take the damage? Or does player1 have to declare the teleport after the successful attack but before the damage is known?

Emboldening Bond 1st-level Peace Domain feature

You can forge an empowering bond among people who are at peace with one another. As an action, you choose a number of willing creatures within 30 feet of you (this can include yourself) equal to your proficiency bonus. You create a magical bond among them for 10 minutes or until you use this feature again. While any bonded creature is within 30 feet of another, the creature can roll a d4 and add the number rolled to an attack roll, an ability check, or a saving throw it makes. Each creature can add the d4 no more than once per turn.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Protective Bond 6th-level Peace Domain feature

The bond you forge between people helps them protect each other. When a creature affected by your Emboldening Bond feature is about to take damage, a second bonded creature within 30 feet of the first can use its reaction to teleport to an unoccupied space within 5 feet of the first creature. The second creature then takes all the damage instead.